SEED GERMINATION ECOPHYSIOLOGY OF JEFFERSONIA DIPHYLLA, A PERENNIAL HERB OF MESIC DECIDUOUS FORESTS

Abstract

Freshly‐matured seeds of the mesic deciduous woodland herb Jeffersonia diphylla (L.) Pers. (Berberidaceae) have underdeveloped (ca. 0.6 mm in length) embryos and exhibit deep, simple morphophysiological dormancy (MPD). For rapid growth of the embryos at October (20/10) and November (15/6 C) temperatures in October and November, seeds must first be exposed to high (30/15 C) summer temperatures. If embryo growth is not completed in autumn, it continues during winter. However, even after 10–12 weeks at summer temperatures, embryos grew very little at 5 C, unless growth already had begun at autumn temperatures. After embryo growth has been completed, or after it has been initiated, seeds require cold stratification (5 C) to overcome dormancy. Embryos must attain a minimum length of about 1 mm before seed dormancy can be broken by cold stratification. Gibberellic acid increased the rate of embryo growth in seeds kept at 20 C, but only 1–9% of them germinated. Thus, GA substitutes for warm but not cold stratification. High summer temperatures, as well as the traditionally‐used autumn and winter temperatures, should be used in germinating seeds with deep, simple MPD.